In the construction of an asphalted road, under which a plastic pipe is laid, on a roadbed to prevent a road from being snowed up or frozen, there is used a method wherein wire netting is first laid on a roadbed, a plastic pipe is laid on and fixed to the wire netting, asphalt concrete heated to 150.degree. to 220.degree. C. is fed from an asphalt finisher onto the roadbed and leveled to thereby bury the plastic pipe in the asphalt concrete, and the formed asphalt concrete layer is rolled with a roller under a load of 10 to 20 tons.
The pipes of plastics such as crosslinked polyethylene and nylon are used as the heating plastic pipes.
In the construction of an asphalted road having a heating plastic pipe laid thereunder in the manner as mentioned above, there are caused disadvantages that the plastic pipe is softened by the heat of asphalt concrete fed onto the roadbed and waves by thermal expansion, or the softened plastic pipe is crushed or deformed by a rolling load when the asphalt concrete layer is leveled with a roller, and the pipe becomes unusable.
To solve the problems, there has been proposed an construction method wherein when asphalt heated at a high temperature is deposited, a cooling medium is allowed to flow through the plastic pipe previously laid on the roadbed to thereby prevent the above-mentioned disadvantages from being caused, for example, to prevent the plastic pipe from waving by thermal expansion or prevent the plastic pipe from being softened and crushed during pavement works comprising depositing asphalt [see, JP-B-52-40133 (The term "JP-B" as used herein means an "Examined Japanese Patent Publication")].
In the above construction method wherein the pipe is cooled with a cooling medium, the waving by thermal expansion or crushing can be prevented to some degree when a pipe of a plastic material having a high softening temperature such as nylon is used. However, when a pipe of a plastic material having a low softening temperature such as crosslinked polyethylene is used, an effect of preventing the pipe from being softened and crushed is insufficient.
This invention has been accomplished with the view of solving the problems associated with the prior art as mentioned above.